Dear Cemolcay,
I've using this project to create my own custom keyboard. But my problem is I can not see my language on button key. It just shown "?", please see the screenshot below.

I am also following as your guide. I try to add custom font to see my own language and then I am trying many ways to use custom font on keyboard. But I can not fix it.
Please help me to use custom font on Keyboard.
Best,
SaiTawng Pha